Threading Aluminium

[The Mighty Volt]

Hi there.

I want to build my A123 pack into the triangle of the frame.

In order to add "depth" to the triangle, I will augment the existing frame by welding aluminium bars of a certain thickness to the existing frame on either side of the cross bar and diagonal and upright. The thickness will be such as allows me to fit in the packs but also allows me to still pedal.

I then want to drill holes into these new bars, and thread them, allowing me to screw and unscrew sheets of aluminium, steel or pvc which I will use to enclose the triangle on both sides, allowing me to enclose and re-open the triangle at will, from either side, to access the battery.

Does anyone here have any advice on how to thread holes which have been drilled into aluminium?

I have seen one trick where existing threads can be repaired using aluminium "welding rods" which are melted into the hole, and then a steel bolt is pushed into the molten material in the hole. This is then allowed to set hard and the bolt is simply screwed back out, leaving a neatly threaded hole. However, I am not sure if this is for thread repair or whether it will give new threads where none had previously existed.

Here is the link to the above-mentioned method.: http://www.youtube.com/watch?v=843jjv58BCA&feature=related

Thanks, as ever.

 

[FeralDog]

Why not use a Blind Nut Rivet ?
Easier.
http://www.emhart.com/products/pop/popnut.asp

 

[The Mighty Volt]

Why not use a Blind Nut Rivet ?
Easier.
http://www.emhart.com/products/pop/popnut.asp

Wow. That looks easier alright.

Before you showed me this, I was going to give these a go, they are called "Time Sert".....http://www.youtube.com/watch?v=Gxnm8J9WXz8&feature=related

With "Time Sert", you destroy the existing damaged thread, so it would work where there was no thread in the first place. You cut a little counter sink, tap the hole, and insert a threaded column which sits into the new threads. This thread is steel, which means you can tighten as much as you like.

 

[FeralDog]

The "time sert" looks like a version of the old Heli-coil "http://www.emhart.com/products/helicoil.asp.
Both of those systems are used for assembly where precision, differential heat, and torque is much more critical than your access covers.
Blind nuts come in all sorts of configurations, I used one type (can't remember the name) that was simple screw-in (no rivet gun) and it expanded a sleeve of rubber.
Blind nuts are common on shrouds, access covers, things that don't need a super amount of holding strength to mate.
Google till ya find the ones you like.
Good Luck!

 

[The Mighty Volt]

The "time sert" looks like a version of the old Heli-coil "http://www.emhart.com/products/helicoil.asp.
Both of those systems are used for assembly where precision, differential heat, and torque is much more critical than your access covers.
Blind nuts come in all sorts of configurations, I used one type (can't remember the name) that was simple screw-in (no rivet gun) and it expanded a sleeve of rubber.
Blind nuts are common on shrouds, access covers, things that don't need a super amount of holding strength to mate.
Google till ya find the ones you like.
Good Luck!

Cheers 'Dog, thanks for your help. What system are you running yourself??

 

[FeralDog]

TMV;
If you mean my battery system , well it is Caveman SLA's . I am working towards a spiffy leather bag for them though ... :lol:

Thus I may have another small tip for ya. IF your aluminum frame is just a "cradle" for your batteries, and doesn't need to be super-welded for flexing and a robust hold ...well , have you thought of simply bonding (Like Loctite structural adhesive, or epoxy) the aluminum , or even riveting the aluminum battery framework to the frame?
The reason I ask is that welding aluminum can be tricky (heat, thickeness, etc).

 

[The Mighty Volt]

TMV;
If you mean my battery system , well it is Caveman SLA's . I am working towards a spiffy leather bag for them though ... :lol:
Other systems of "interest" to me are my odd boats, and Oh,-- I spend a few weekends every-now-and-then watching these guys http://www.eaa.org/, and these guys work http://www.confederateairforce.org/, and sometimes a few of these guys too http://www.boeing.com/.

Thus I may have another small tip for ya. IF your aluminum frame is just a "cradle" for your batteries, and doesn't need to be super-welded for flexing and a robust hold ...well , have you thought of simply bonding (Like Loctite structural adhesive, or epoxy) the aluminum , or even riveting the aluminum battery framework to the frame?
The reason I ask is that welding aluminum can be tricky (heat, thickeness, etc).

I have thought about the methods you mention......I suppose I could get away with bonding, there might be no need for the welding, but I would still want to use threaded bolt holes as at least one side of the triangle is going to be opened and closed routinely. But yes, for the purpose of augmenting the frame with the aluminium additions, I suppose some sort of a glue could be used. Does Aluminium have a reputation for adhering to itself with just basic epoxy? Thanks for the tip.

 

[rkosiorek]

the common commercial brand is Rivnut. another is Rivetnut. for either a local or online supplier google is your friend.

you don't need a special tool to install these. you can do it yourself using a a bolt a nut and a washer. you'll also need a couple of wrenches.

the bolt is the same size as the Rivnut. thread on a nut. apply some grease to the washer on both sides and slide it onto the bolt. thread on the Rivnut until it is snug against the nut. drill the right size hole. insert the Rivnut. use one wrench or vicegrip to keep the bolt from turning. using the other wrench turn the nut to squeeze the rivnut. do not over tighten and strip the rivnut. you want to make sure that only the nut turns. that is the reason for the greased washer separating it from the rivnut.

rick

 

[The Mighty Volt]

the common commercial brand is Rivnut. another is Rivetnut. for either a local or online supplier google is your friend.

you don't need a special tool to install these. you can do it yourself using a a bolt a nut and a washer. you'll also need a couple of wrenches.

the bolt is the same size as the Rivnut. thread on a nut. apply some grease to the washer on both sides and slide it onto the bolt. thread on the Rivnut until it is snug against the nut. drill the right size hole. insert the Rivnut. use one wrench or vicegrip to keep the bolt from turning. using the other wrench turn the nut to squeeze the rivnut. do not over tighten and strip the rivnut. you want to make sure that only the nut turns. that is the reason for the greased washer separating it from the rivnut.

rick

Thanks Rick- sounds like a cheaper more generic version of the SERT...which seemed aimed at pros. Cheapest SERT's I was coming up with were $60+. I will google and post results. Ta.

 

[FeralDog]

I suppose some sort of a glue could be used. Does Aluminum have a reputation for adhering to itself with just basic epoxy? Thanks for the tip.

Yes, it has quite a good reputation for bonding with the proper adhesive. Good clean surface preparation sure helps.

Epoxies are even better now! Many magnets in motors are bonded by structural epoxies.
Loctite (Speedbonder Series ), 3-M , Devcon are major world-wide companies that make the mostly 2-part epoxies, and what you may reference are called "structural adhesives" for bonding metals/aluminum. {http://www.enewsbuilder.net/HenkelTechTalk/e_article000690733.cfm?x=b11,0,w} AND {http://www.adheredist.com/products/structural_adhesives/scotchweld_structural.htm}
Your local hardware, or automotive store may even have a name brand structural adhesive for your Al use. Price IS a good indication of quality in this subject. Good major-name structural adhesives range from about $15-$60 USD per small bottle.
I had pretty good luck with 3M DP-420 (w/rivet), but your fabrication will surely vary.
Also, I have seen adhesive double-sided 3M tape used too! Very strong bond, I could not get it apart. http://solutions.3m.com/wps/portal/3M/en_US/VHB/Tapes/
My unsolicited advice for an amateur starting out a build is to try and re-enforce any structural adhesive bond with a pop-rivet (or several) for extra safe and secure fastening. Rivets + structural adhesives make a very strong bond, and rivets will hold the pieces together while curing too.

Finally, back to blind nuts, they come in all sorts of configurations and generally are designed for "pull out" strength. The lightest & common are those fasteners akin to fasteners that hang a picture on a wall. Then, they go up to simple brass and nylon like http://cgi.ebay.com/ws/eBayISAPI.dl...f2daba7&itemid=370299839949&ff4=263602_263622, anyways >>> when it comes to your design , ask yourself what you think is the force of "pull out" of the cover you are making, and then use the appropriate threaded inserts, or blind nuts, or simple studs with wing-nuts, or even plastic cable ties for your access cover .....
A note on Aluminum. Since Aluminum has more of a tendency to fatigue (cycles) than steel alloys, I have always had a weird way of checking all my welds and bonds whenever I clean my bikes, that aluminum can be a pesky material .... :wink:

 

[rkosiorek]

SERT's are a little different. SERTS are called threaded inserts and have threads on the inside and the outside. the intention is either to repair a damaged thread or to make a stronger thread in a softer material.

to instal a SERT you drill and tap a hole. then you screw in the SERT. the SERT is locked in place by some type of adhesive that is painted on the outside for the cheaper ones.

the ones you pointed out in your post are really fancy ones. they have a slot cut through the wall and a piece of nylon is stuck through the slot so that when you put in the screw that one piece of nylon contacts both the inner and outer threads locking them both at the same time. nice things about these is that they are easily removable without damaging the threads in the soft material. but they are expensive. and they are inttended as single use. when you put in the screw it cuts threas into that piece of locking nylon making it less and less effective each time.

they don't realy apply for your use though SERTS and threaded inserts need to be threaded into the base material at least 1.5X the diameter of the screw. they are meant for fairly thick material. Rivnuts are meant to provide blind hole threading in material too thin to tap. frame tubes usually fit into that category of "too thin to tap."

the inexpensive plastic butterfly ones need a hole much larger than the target screw and with repeated assembly/disassembly are prone to turning. ie. when you try to unscrew it the plastic part spins in the hole, making it impossible to remove unless you pull it out.

rick

 

[The Mighty Volt]

Yeah thats it the last thing I want is soft stuff getting turned and worn. :x My brother is a mechanic so I might see if he can get me any of this stuff at trade prices before I do any deals online. Cheers.